20 practice MCQs on concentration units, solubility, colligative properties and Raoult's law. Every question has the correct answer and an explanation.
Start free — 20 questionsSolutions is part of the MDCAT Chemistry syllabus. This page collects Solutions MCQs in the style of past MDCAT papers — below are 12 of them with answers and explanations, and the full set of 20 questions is in the HighYield MDCAT QBank.
This chapter covers: concentration units, solubility, colligative properties and Raoult's law.
Correct answer: D. Decreases
As the number of dissolved solute particles increases, the freezing point of the solution decreases, a colligative property called freezing point depression.
Correct answer: C. 100.052 °C
Using the boiling point elevation formula with the given mass of glucose in 1 kg of water, the calculated boiling point of the solution is approximately 100.052°C.
Correct answer: D. Common ion effect
Adding NaCl to a solution containing AgCl increases the concentration of the common chloride ion, shifting the equilibrium and causing AgCl to precipitate out due to the common ion effect.
Correct answer: A. Elimination
Reaction of a haloalkane with alcoholic KOH/NaOH proceeds by an elimination mechanism, removing HX to form an alkene.
Correct answer: A. Calcium oxide
Calcium oxide (quicklime) is used to remove the remaining water from rectified spirit to produce absolute (100%) alcohol, since it reacts with and absorbs water.
Correct answer: B. Acetic acid
Acetic acid is correct because it is commonly used for seasoning food. Acetic acid, also known as vinegar when diluted, is a weak acid that adds a sour flavor to foods and is widely used in cooking and food preparation.
Correct answer: A. Acetic acid
Acetic acid is used: i) as a coagulant for latex in rubber industry. ii) in the manufacture of plastics (polyvinyl acetate) rayon (cellulose acetate) and silk. iii) in medicine as a local irritant. iv) as a solvent in the laboratory for carrying out reactions. v) in the manufacture of pickles.
Correct answer: C. Common ion effect
The decrease in solubility of a salt in a solution that already contains an ion common to the salt is known as the common ion effect. This effect occurs because the presence of the common ion reduces the solubility of the salt by shifting the equilibrium towards the solid form.
Correct answer: B. Glucose
Typically, glucose forms a six-membered ring called a pyranose. This ring consists of five carbon atoms and one oxygen atom.
Correct answer: B. Cu2O
The blue color of Fehling's solution changes to red when warmed with an aldehyde due to the formation of Cu₂O (copper(I) oxide) because of the reduction of Cu²⁺ ions present in the solution.
Correct answer: D. Zinc has smaller reduction potential than copper
Option D is correct because zinc’s smaller reduction potential (-0.76V) compared to copper’s (+0.34V) signifies that zinc is more reactive. In electrochemical terms, a metal with a lower reduction potential can displace a metal with a higher reduction potential from its compound in solution. Therefore, zinc can easily displace copper from its solution. Option A is incorrect because the atomic number does not dictate the reactivity of metals. Option B misstates the relationship between the reduction potentials, as zinc's is lower than that of copper. Option C, while potentially true in some contexts, does not pertain to the displacement reaction, as reactivity is the determining factor.
Correct answer: A. Mole fraction of solute
In Raoult's Law, the lowering of vapor pressure of a solvent in a solution is directly related to the mole fraction of the solute.
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